Spin Susceptibility and Superexchange Interaction in the Antiferromagnet CuO

Evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO is presented in a framework of Heisenberg model. We have obtained an experimental absolute value of the paramagnetic spin susceptibility of CuO by subtracting the orbital susceptibility separately from the total susceptibility through the $^{63}$Cu NMR shift measurement, and compared directly with the theoretical predictions. The result is best described by a 1D $S=1/2$ antiferromagnetic Heisenberg (AFH) model, supporting the speculation invoked by earlier authors. We also present a semi-quantitative reason why CuO, seemingly of 3D structure, is unexpectedly a quasi 1D antiferromagnet.Comment: 7 pages including 4 tables and 9 figure

ARPES: A probe of electronic correlations

Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct methods of studying the electronic structure of solids. By measuring the kinetic energy and angular distribution of the electrons photoemitted from a sample illuminated with sufficiently high-energy radiation, one can gain information on both the energy and momentum of the electrons propagating inside a material. This is of vital importance in elucidating the connection between electronic, magnetic, and chemical structure of solids, in particular for those complex systems which cannot be appropriately described within the independent-particle picture. Among the various classes of complex systems, of great interest are the transition metal oxides, which have been at the center stage in condensed matter physics for the last four decades. Following a general introduction to the topic, we will lay the theoretical basis needed to understand the pivotal role of ARPES in the study of such systems. After a brief overview on the state-of-the-art capabilities of the technique, we will review some of the most interesting and relevant case studies of the novel physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental Techniques", edited by A. Avella and F. Mancini, Springer Series in Solid-State Sciences (2013). A high-resolution version can be found at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf. arXiv admin note: text overlap with arXiv:cond-mat/0307085, arXiv:cond-mat/020850

A high-pressure study of Ti3O5Ti_3O_5 by X-ray diffraction and synchrotron radiation. 1. Pressures up to 38.6 GPa

High-pressure X-ray diffraction studies have been performed on powder samples of [beta]-Ti3O5 (C2/m) for pressures up to 38.6 GPa using synchrotron radiation and a diamond-anvil cell. The compressibility is highly anisotropic. Thus, the compression [Delta]l/l0 for the maximum pressure investigated is 5.4, 0.8 and 6.7% for the unit-cell axis directions a, b and c, respectively. The anisotropy is reasonable, considering the crystal structure. The bulk modulus B%_0%, determined from the Murnaghan equation, is 173(10) GPa and B'0 is 7(1)

A high-pressure single-crystal X-ray diffraction study of copper oxide using synchrotron radiation

The crystal structure and lattice parameters of single crystal CuO have been studied up to 80 kbar using a new high-pressure diamond anvil cell and synchrotron radiation

High-pressure phase of the cubic spinel NiMn2O4\mathrm{NiMn_2O_4}

It has been observed that the fcc spinel NiMn2O4 transforms to a tetragonal structure at about 12 GPa. The tetragonal phase does not revert to the cubic phase upon decompression and its unit-cell constants at ambient pressure are a0=8.65(8) and c0=7.88(15)Å (distorted fcc). Within the experimental uncertainty, there is no volume change at the transition. The c/a ratio of the tetragonal spinel is almost independent of pressure and equal to 0.91. The phase transition is attributed to the Jahn-Teller-type distortion and the ionic configuration can be assumed as (Mn3+)tetr[Ni2+Mn3+]oct.The bulk modulus of the cubic phase is 206(4) GPa